In the modern age, in which the technological development changes with each passing day, many innovative and practical electronic apparatuses or lighting apparatus are required. In this regard, power conversion circuits play an important role in, for example, the apparatuses applying power supplies such as computers, lighting lamps and so on. Conventional power conversion circuits can be implemented by three approaches, i.e., constant voltage control, constant current control, and constant power control. In the approach of constant voltage control, the output power is decreased as the output impedance increases. In the approach of constant current control, the output power is increased as the output impedance increases. If the output power is controlled by simply adopting the approach of constant voltage control or the constant current control, the cost is relatively low and the circuit design is relatively uncomplicated, but the power is easily varied and damages the elements.
The approach of constant power control can improve the problems caused by constant voltage and current control approaches, which controls the overall power generated at the load side. However, a conventional constant power control apparatus controls the output power by using high-cost multipliers or accumulators, so that the circuit complexity and the cost are increased. Taking microprocessors provided by a company of Micro Chip as an example, a chip without multiplier charges about 1 USD, while a chip with multiplier charges at least about 2.5 USD. As for a digital signal processor (DSP) provided by Texas Instruments (TI), its price is further about 8 USD or more. An integrated circuit (IC) of multiplier labeled with AD633 and provided by a company of Analog Devices, which is commonly used in the market, charges about 5 to 8 USD. As such, if a product applies these kinds of constant power control apparatus, its cost is increased greatly.